(1) Field of the Invention
The present invention relates to a mounting structure for mounting, into a frame, a bearing member supporting a rotary shaft, and to a fixing device and image forming apparatus using the mounting structure for the bearing member.
(2) Description of Related Art
An electrophotographic image forming apparatus transfers a toner image formed on a circumferential surface of a photosensitive drum onto a recording sheet, and then performs thermal fixing by way of passing through a fixing nip formed between a heating roller and a pressurising roller of a fixing device.
Ordinarily, in the fixing device, the nip pressure (pressure in the fixing nip) between the heating roller and the pressurising roller is made sufficient so as to prevent improper fixing when the toner image on the recording sheet is heated in the fixing nip. When the fixing operation is not performed, the pressurising roller and the fixing roller are separated using a cam mechanism or the like in order to prevent elastic deformation of the rollers.
Incidentally, given that the nip pressure between the pressurising roller and the fixing roller is quite great, strong forces must be applied to execute the pressing and separation of the rollers. Particularly, when the rollers are pressed together or separated, a powerful impact force is applied to the rotary shaft of each roller, to the drive shaft of the cam, and so on. When there is backlash between a bearing member and the mounting hole in which the roller is mounted, a problem arises in that noise is produced due to the impact on the component having backlash.
In order to avoid this problem, for example, the occurrence of backlash is preventable by inserting the bearing member into the mounting hole through a collar or the like, with powerful pressing force, and fixing the bearing member in a state where the entire circumference thereof is pressurised by the inner circumferential surface of the mounting hole.
However, in such situations, the entire circumference of the collar is subject to intense compression, and as such, the radial density thereof becomes extremely high. Thus, an impact applied to the rotary shaft is hardly attenuated, and is propagated to the support frame. As a result, noise is produced by vibrations in the support frame, and these vibrations may have a negative influence on image formation operations if further propagated to the support frame of an image forming unit.
These problems, which occur due to mechanical vibrations in rotary components, occur not only with compression and separation in the fixing device but also, for example, when vibrations generated as the gears of a drive transmission mesh together are propagated to the support frame via the bearing member, and the like.